The Fourdrinier paper making process and machine involves a travelling screen or fabric onto which is fed an aqueous dispersion of cellulosic fibers. The screen is moved over suction and dewatering devices to pull water through the screen and leave the fibers on the top of the screen to form a thin wet web of fibers that is peeled from the screen and transferred to a travelling felt which conducts the wet web through press rolls and a finishing section involving steam heated drying cans and calender rolls to produce a continuous sheet of paper. Such a machine and process tends to orient most of the fibers in the direction of movement of the travelling screen or fabric, and this produces a paper which is strong in the direction of oriented fibers and weak in the normal direction. While such unbalanced strengths may be acceptable in some application, e.g., newsprint, it is not acceptable for other uses, e.g., wrapping paper, bag production, etc.
Attempts have been made to solve this problem by shaking the travelling fabric or by using fluted suction box rolls that are operated at some speed other than that of the travelling fabric. See, for example, U.S. Pat. No. 2,092,798 to Charlton; U.S. Pat. No. 2,095,378 to Charlton; and U.S. Pat. No. 4,306,934 to Seppanen. None of these solutions has been completely successful, and the fibers continue to exhibit too much orientation to provide a desirable strength in all directions.
In German Offenlegungsschrift 1,611,761 published Jan. 28, 1971, there is a disclosure that, at first glance, appears to be closely related to the present invention in that the patentee uses grooved rolls in a Fourdrinier paper making machine immediately downstream from the headbox where the fibers are being formed into a wet sheet. The manner in which the grooved rolls of this prior art patent are used and their purpose are greatly different than is the case with the rolls of this invention. The patent teaches the use of very small grooves and spacings between grooves to produce increased drainage of water through the Fourdrinier screen when the rolls are driven oppositely to the screen. This invention uses considerably larger (3-6 times larger) grooves and spacings to impede the drainage while the rolls are turned at substantially the same speed and in the same direction as the movement of the Fourdrinier screen.
It is an object of this invention to provide a novel paper making process and dispersion roll for use in that process. It is still another object to provide a roll that shows remarkable improvement in maintaining a random orientation of fibers in a paper making dispersion just prior to web formation. Still other objects will appear from the more detailed description which follows.